Touch screen technology has become an important component of many modern electronics, such as tablet computers and cellular phones. Typically, touch screen technology incorporates the use of resistive or capacitive sensor layers which make up part of the display. Screens for devices which utilize such technology are often prone to damage due to the increased level of direct contact by the user with the screen. Such damage typically includes both scratching and breakage of the screen itself depending on the materials used and the use thereof. As a result, resistive and capacitive touch sensors usually include translucent electrical insulating covers placed on top of the display structure in order to protect and isolate the touch sensor panel from environmental conditions, abrasion, oxygen, and harmful chemical agents.
Resistive and capacitive touch screen technologies require materials that are both transparent and conductive to be functional. Indium Tin Oxide (ITO) is currently the most widely used metal oxide for touch screen sensor applications because it is optically transparent and is has fair conductive properties. ITO is commonly employed to make transparent conductive coatings for liquid crystal displays, flat panel displays, touch panels, solar panels and aircraft windshields. In resistive touch screens, when a user touches the screen with a finger or a stylus, the ITO film is pushed into contact with the ITO glass producing a voltage signal allowing a processor to compute the coordinates of the touch event and process the appropriate response to the touch point. Although the use of ITO is a well-known and accepted technology, it is not ideal. The main issues with ITO are the limited supply and the rising cost of indium, in addition to its fragility, lack of flexibility and low conductivity compared to other metals.
As previously stated, it is typical to employ glass or polyester layers as protective covers in touch screen panels. Polyester films, while flexible, can only provide a minimal level of hardness. Specifically, such films provide a surface harness ranging from about 2H to 4H. As a result, polyester films are susceptible to scratches. On the other hand, glass covers, which are able to produce pencil hardness readings above 7H, do provide very good scratch protection. However, such glass covers do not provide a high level of flexibility and are therefore susceptible to breaking upon impact with a hard surface.